1. Field of the Invention
This invention relates to abrasive tools, and more particularly to grinding wheels and methods adapted to replace milling operations used for the removal of large quantities of material from the surface of workpieces.
2. Background Information
Components intended for complex, precision assemblies such as automobiles and other industrial products must often be manufactured to stringent quality standards, including tight dimensional tolerances and surface finish requirements. Some of the tightest standards are associated with the manufacture of vehicular components. In the initial finishing step, these components are generally machined by common processes such as fly cutting or high speed milling using milling heads having hardened ceramic inserts, such as silicon nitride, tungsten carbide or polycrystalline diamond (PCD). To help insure that the finished surface is adequately smooth and flat following machining, a multi-step approach is often used, which includes a rough pass and one or more finish passes with precision grinding tools. With new high speed machining centers, coolant is supplied at relatively high pressure and low volume through the spindle (through an axial bore) to the center of the cutting head. Because machine cutting processes are very slow, compared to grinding processes, the nature of the coolant delivery system is not critical to the effectiveness of the cutting operation.
These milling processes have been used to make vehicular engines, transmission components, pump housings, solenoid valves, power steering components and bearing and mating faces for use in automobiles and other vehicles, appliances, machines and other manufactured items. In general, machine tool cutting processes (also known as “machining” or “milling”) have been used in any application or operation where the workpiece must have a precision flat, parallel surface. In nearly all of these applications and operations, the milling process must be followed by a grinding process to reduce surface roughness to a finer level than one can achieve with a milling process.
In many operations, the workpieces have had to be further processed, such as with a cup-type face grinding wheel on a conventional grinding machine, to meet these standards. Disadvantageously, this extra grinding step, including the extra tool change and set up, tends to increase the time and expense of workpiece fabrication.
One attempt to reduce the number of discrete fabrication steps has involved equipping the milling machines with grinding wheels in lieu of milling cutters to carry out a surface grinding step in lieu of a face milling step. In this manner, it was anticipated that both the rough and finish milling operations could be eliminated in favor of one or more grinding operations, to therefore eliminate the need for extra tool changes, multiple tool setups, etc. A drawback of this approach, however, is that the relatively high pressure, centrally (i.e., spindle) fed coolant flow provided by the milling machines tends to be incompatible with grinding wheels, which typically rely on lower pressure, peripherally fed coolant flow.
A need therefore exists for an improved tool and/or method for effecting grinding operations using conventional spindle-cooled milling machines.